Approximately 40% of patients who are hospitalised for pneumonia develop a parapneumonic effusion 3.
Fluid leaks into the pleural space due to increased permeability of the visceral pleura adjacent to the infected lung. Bacterial cases of pneumonia are a more common cause of parapneumonic effusions than viral cases of pneumonia 3.
Plain radiograph and CT
Similar findings to a simple pleural effusion 1:
- usually small volume
- normal meniscus sign
- no loculation
- "split pleura sign" is not typical and more specific for empyema
Treatment and prognosis
Parapneumonic effusions often resolve with the treatment of the underlying pneumonia. However, ~7.5% of patients with parapneumonic pneumonia progress to a fibrinopurulent stage such as empyema 3.
- 1. Webb WR, Higgins CB. Thoracic Imaging. Lippincott Williams & Wilkins. (2010) ISBN:1605479764. Read it at Google Books - Find it at Amazon
- 2. Kraus GJ. The split pleura sign. Radiology. 2007;243 (1): 297-8. doi:10.1148/radiol.2431041658 - Pubmed citation
- 3. Sahn SA. Diagnosis and management of parapneumonic effusions and empyema. Clin. Infect. Dis. 2007;45 (11): 1480-6. doi:10.1086/522996 - Pubmed citation